Coach Mike Tomlin expects his quarterback to play on Sunday when the struggling defending AFC champions host Tennessee (3-1).

The same can't be said for linebacker James Harrison, who needs surgery to repair a fractured orbital bone near his right eye and will be out "for a number of weeks."

Harrison sustained the injury in the third quarter of Pittsburgh's 17-10 loss to Houston last week when the forepad in his helmet came down and struck him in the eye as he collided with a Texans player.

The 2008 NFL Defensive Player of the Year returned to the game, but was ineffective at times as Houston drove the length of the field to score the winning touchdown.

The 33-year-old groused the Steelers (2-2) "stink" afterward but gave no indication of significant damage. Tomlin indicated he won't know how long Harrison will be out until after the surgery.

The Steelers will slide Lawrence Timmons over from his inside linebacker spot to replace Harrison and start veteran reserve Larry Foote in Timmons' place.

Not exactly the way the Steelers wanted to start a pivotal stretch. They have been manhandled in losses to Baltimore and Houston and were relatively unimpressive in wins over woeful Indianapolis and Seattle.

Tomlin stressed the need to return to fundamentals after his team allowed Houston's Arian Foster to rack up 155 yards, the most the team has surrendered to a single back in nearly eight years.

Getting back to basics while putting familiar faces in somewhat unfamiliar places will be difficult, though the defensive line should get a jolt from nose tackle Brett Keisel.

The veteran is expected to play after missing the past two weeks with a knee injury. Yet Tomlin isn't hailing Keisel's presence as reason to think the defense's problems stopping the run are over.

"We have capable men who play who need to do a better job," Tomlin said.

And do it better quickly.

The Steelers are second in the league in yards allowed but are 22nd against the run, giving up a whopping 4.8 yards per carry, well above the 3.0 yards per attempt they gave up last season.

"There's a fine line between performing well and substandard," Tomlin said.

"Some of the mistakes are mental, some of them are physical. They're not centrally located in one person or position but when you add those things over the course of a football game you get 8-10 snaps where somebody is letting you down either mentally or physically and you have an opportunity to give up some big yards."

It's the kind of opportunities the offense hoped it would have this season. It hasn't happened. Roethlisberger has thrown three touchdowns and five interceptions and endured a pounding from opposing defenses in the process.

The battered offensive line could take a step toward normalcy if left tackle Jonathan Scott and right guard Doug Legursky return from a shoulder injury.

They'll be charged with providing better protection for Roethlisberger, who injured his left foot on Pittsburgh's penultimate drive.

He stayed in the game but wore a protective boot afterward. An MRI on Monday showed no breaks, though he may be limited in practice early in the week.

Backup Charlie Batch will get a package of plays just in case Roethlisberger suffers a setback, but he played the second half of last season with a fractured right foot and had no major issues.

Whoever is on the field, at any position, will need to respond with the kind of spirited performance the team has lacked at times during the first month of the season.

Still, Tomlin stressed it's the first month. The Steelers are concerned, but not panicked.

"We are not going to make something out of this that it's not," Tomlin said. "We understand that we are capable of playing better. We expect to play better. We know where the solutions lie, of course within us, and how we prepare and ultimately how we perform."